Remote control systems



June 2l, 1960 P. K. ECKHARDT ET AL 2,942,238

REMOTE CONTROL SYSTEMS 2 Sheets-Sheet 1 Filed March 8. 1956 June 2l, 1960 P. K. ECKHARDT ETAL 2,942,238

REMOTE coNTEoL sysTEMs 2 Sheets-Sheet 2 Filed March 8. 1956 INVENTORS. Paal E Eckhardt md rzlzur IZ Jackal Y U- L ,W

THEIR ATTRNEY NNN muwwxmv @SENS QTM NNQIT KNNQQ .51m ESE@ |1 im .1 IU smll.. E n@ S n Pihinldh Nw m bbw SN United States Patent f O REMOTE CONTROL SYSTEMS Paul K. Eckhardt, Sharpsburg, and Arthur P. Jackel, Penn Township, Pa., assignors to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Filed Mar. 8, 1956, Ser. No. 570,366

5 Claims. (Cl. 340-163) Y Our invention relates to a remote control system. More particularly, our invention relates to a remote control system in which the proper transmission of control functions is checked at the oflice.

The general system .of the present invention is of the timecode type employing codes of long and short elements which are ltransmitted over a communication channel; For example, the general system of this invention may be that disclosed in Letters Patent of the United States No. 2,442,603, issued June l, 1948 to Arthur P. I-ackel, for a Remote Control System.

In applying remote control systems of this type to varied kinds of installations, special problems frequently arise. One such problem'is to assure that each control step is received properly at the station before the control functions are registered and act to accomplish the corresponding operation of the yapparatus at that station. In other words, a check must be made, at the oce or control location, that no line interruptions or erroneous pulses have distorted the code. Since the communication channel between the oiice and the station or stations may be a direct current line circuit or a carrier channel vof any well known type, these interruptions or erroneous pulses are a matter of some concern. Suchy erroneous action may cause the registry of false controls or at least improper controls which resultl in actions at the station which are, at a minimum, not those designated and which may be rvery undesirable. Thus the check provided at the otiice to assure that the control functions yare properlyl received at the station must be capable Vof halting the code or at least preventing its registry at the selectedstation Since remote control systems of this general type may have progressive registry of the control functions, an instantaneous check as to the correct reception ofthe control code and provisions for immediately preventngthe registry of false control functions arel necessary.

Accordingly, an object of 'our invention is to provide, in a remote control system of this type, means to check the ltransmission of control codes to' assure their proper reception at the stations.

Another object of our invention is to provide, in a remote control system, answer-back facilities from stations to the control oflice which indicate the proper reception of controlcodes during the progress of the code. vIt is .also an object of our yinvention to provide means at the control location in such a system to prevent the registry, of improper control yfunctions at the stations.

Still another object of our invention s topro'vide means at the otice of remote control system, responsive Vto answer-back indications of the improper recept-ion 'of a control code at a station, to halt that control code during its transmission.

A further object of our invention is to provide an arrangement in a remote control system to prevent the registry of improper control functions if a control code ice is distorted by interruptions on the communication channel.

Other objects and features of our invention will be obvious as the specification progresses when taken with respect to the accompanying drawings. A

=In practicing our invention, we provideimeans at each station in a remote control system -to retransmit back to the control or oiice location each control code step as it is received. This retransmitted c ode step may' be a regular code step transmitted over the indication channel if'such a separate channel is in use, or 'the retransmitted code step may be a code pulse on the simplex communication channel superimposed upon the corresponding control pulse or code step. This retransmitted or answer-back pulse is received at the 'oice nearly simultaneously with the transmission of the corresponding control step. The proper reception of this answerback pulse holds energized a code disagreement relay to allow the control code transmission to'continue. If no answer-back pulse or an out-of-synchronism pulse is received at the office, this code disagreementrelay is released and immediately causes the coding action to halt. Depending upon the details of the system involved, the control code may b e halted immediately, that is, upon the existing code step and the system reset to normal. In other cases, the code may be halted only on an odd numbered code step and the system reset then to normal. In either case, the registry of improper control functions at the selected station is prevented and the eiect on the system of communication vchannel interruptions or extraneous pulses is minimized.

We shall now describe two forms of apparatus embodying our invention and lthereafter point out the novel features thereof in the appended claims.

lReferring now to the drawings,

Fig. l shows one form of apparatus-embodying our invention as applied toa remote control system iu which carrier communication channels are used.

In Fig. 2, the form of our invention of Fig.l 1 is shown applied -to a remote Vcontrol installation using a direct current line circuit.

v lIn Fig. 3 of the drawings, a second form of the apparatus embodying our invention is shown which may be used under certain .specializedoperating conditions. In thisdrawing, the remote control system as shown utilizes a carrier communication channel.

Fig. 4 of the drawings shows` the application of the second form of our invention to a remote control system usiuga direct current line circuit.

In each of the drawings, similar reference characters refer'to similar parts of' the apparatus.

It is to be pointed out at this time that a suitable local source of direct current' energy is provided at each oilice and station location shown in the drawings, this power sourcebeing preferably a battery of proper voltage and capacity. However, for the sake of simplicity, these Vpower sources are not shown in thedrawings, their positive and negative terminals Ibeing identied by the conventional reference characters B and N, respectively. In all iigures of the drawings, the movable portion of each neutral relay contact is conventionally illustrated to move up when the corresponding relay winding is energized. In other words, regardless of whether the contact is above or below the wind-ing symbol in the drawing, the upper stationary contact point is the front contact and conversely the lower is the back contact.

In Fig. l, there is showna single sta-tion, remote control system of a well known type which includes apparatus embodying the features of our invention. In Fig.- 1 the otiic'e or control location is shown at the 'left of the ing with the single station at the right. However,

here-noted that our invention is not limited to such single station systems but may be applied to remote control systems having a plurality of stations. Also, while in this present application thefanswerbackracilities are `shown as being applied fromy the station to the oice to checkfthe Vtra;rsinissionand reception of control codes, -it is to be finfther nderst'oodwthat vthe system `ofour-.inventionmay be applied to provide-answer-back.facilities vfrom-arrotiice 'tothe -vario'il's 4stations toichecklthe transmission V`'and vreception :of-indication codes, lespecially where suchcodes may "detailedinformation or'lida'ta which-.must be `:r'operlyrecorded to-lbeof value. f

. ffAs shwnn-iFig'.-1,the ofce and -stationare connected hy a ycarrier communicationchannel. This carrierfchannel-may Abefofany'well known typeand isshown as being of-a-duplex nature having two undirectional carrier circuits. The first 'carrier'circuit is rfrom the Aoiice to the station, that-i's, left-to-rght, `and the second .fronti-he. station'to Ithe-oiiice, that is, right to left. Therst circuitY uti- -lizes a carrier Acurrent havingaffrequency F1, while the vsecond carrier circuit utilizesassimilar carrier current-having a frequency F2. Carrier cprrent of frequency F1 is produced-incarrier transmitter -Fl and-vis-received by the -Fl carrierreceiver-at thestation. Similarly, carrier current of Afrequency FZ isproduced bythe-F12 carrier transmitter at the station Vlande-isreceived :by the F-Zcarrier receiver-at theofiice. -rBothlcarri/er currents are normally on during Ythe -at-rest -condition of the system The carrier vcircuits -maysbe--superposedon physical line circuits An or- Imally usedWfor-'other types of communication 'or may .be carried Vlay-radio ormicrovvave channels. Detailsot the *carrier-transmitters,receivers, and the channels used are herein show-n conventionally, as they are not part of our invention, suchapparatus being well known to the lart and any -one of several different types :may lbe used with the Sym ` The oce location is'provided with an oiiice coding unit shown conventionally by the dotdash box designated VQCU. The system of o'u'rinvention s'applicable to -any of several wel-l known types o'f time code remote control systems. v`For example, the basic system used may be that lshown inthe previously mentioned Patent y2,442,605 or 'it may be similar tothe system shown in vthe instruction pamphlet Manual'No. 510 entitled, Time Code Control System, published by the AUnion Switch lrS-Signah Divisionof Westinghouse Air Brake Company, in November Y1944. Since the-basic remote controlY apparatus is shown in detail in these publications,only'suchdetails o'f lthe 'basic system are herein-shown as 'are 'necessary for an understanding of our invention, r'efere'ncebeing made 'to the. previouslyv 'mentioned publications A-for 'a complete 'description of the 'operation of'the-codingunits. i v v Ifhe coding unit OCU v'includes `a master re'ly OM which is energized duringa'ooitrolcoile in the ma'nner `shown in theprevonsly :mentioned publications. It' is siiincciit 'Here` ro- 'understand thatjrelsy V'OM- is .energized 'ndpi'ck's ''p'to initiate aco'ntrol'cie. '-Thi's' relay is :linen her'rrenergizdlimingthe entire contini code, 'reteas- 'ing duriiigtheni code'siep. Further, vrelsyOM is not 'energized 'and-remains released-during indication codes. The o'c'e `location is also supplied with-a 'master relay repeater relay MP,`which'is energized' from'termi'nal B of the 'sorcelhrough front 'contactc` of relay OM and 'the 'winding -of kr'elaylY/I'P` t'o 'terminal N. Relay MP' thu's picksfupuand 'remains'up fdu'ri'ng an 'entire control code.

puit-OCU 'is 'also provided' withtw'o 'transmitter relays '01T"an'd"02T. Each of'thes'e r'e'l'a'yslis of a slow release "type and its release is further retarded bythe use -of a 'rectifier snub. An energizing circuit forr'elayolT is completed over front contact a of relay M at the '-.beginning of a control fcode, this pickup circuit also including backcontact-b of relay 02T. vrRe'lay'Z'T is energized'by a circuit which` is completed from terminal B over i Vfront contactb of-rel`ayOM, rfront contact cY of relay (T, and 'thelwind'ing of rely 02T 4tolterrtiinawl `'Each of :the

- 4 transmitter relays has one or more stick circuits completed over front contacts of the corresponding relay. These stick circuits, as well as theinitial energizing circuit for relay 01T, are shown in detail in the previously mentioned Patent 2,442,603 and need not be further discussed herein. p

Briey reviewing, the character of each transmitted impulse or code step-isdeter'rrnnedfiny the interval of time during which transmitted relay 01T is eitheriipicked up orrelease'd. .Itisto-benoteld thatthis relay isf-alternately .picked up andrclcascd toproduce the short codesteps by back contacts of the odd numbered counting chain relays of .the coding unit. Relay 02T ispicked up each time relay'ilT picks up to V'close its Vfront contact c. It is obvious that rel-ay 01T cannot pick up, however, until relay 02T has released, and thus the even numbered short code steps are controlled by the release time of relay 62T. When van odd numbered code -step'is/to'be long, relay 61T is held'energiz'ed 4by venergyoverone of its 'stick circuits '-'fromz'thel control functioncontact assigned to that particular code step. Likewise, vwhen'atreven --nurrrbered code-stepfis tobe lon'g, relay 02T :is held -ener- `gized overits stick 4circuit-rbye`ner-gy from the-control function contact assigned to that-code step. Thus'the charactertistics of-control'code are determined bythe 0p- 'erat-ion of these xtwoztransrnitter relays.A

In the systemrof 'our invention, reach of `these transmitter relays is providedzwithran additional stick circuit. Forexatnplegrelay @ZT maybe held energized-by a circuitfrom terminal B 'over back contact'b of code Ydisagreement relay CD,-.trontreontact a, andthe wiudingvof .relay v462T to termina-LN. Likewise, a similar circuitlfor relayvtllf includes backcontact c ofvfrelay -CD and front contacts `a and b of relay 01T. Tllreuse of--these :special stick circuits =will `be discussed more fully hereinafter. i The olice is-also ysuppliedwitlrali-ne 4relay O-R' which isof 'the biased type as indicated -by `the arrowshown inside thefsymbol -forvthey relay winding. This relay, as well as other simil-arsrelays shown, -picksup .to close front contacts only when energizedbycurrent ilowing-in the direction of the arrow. Relay OR repeats the code .pulses Y receivedlover the communication channelorcgenerated locally.. During indication codes, for example, this relay is Venergized at times by the vcircuit traced .from terminal` B. overftront contact-bjof -office carrier receiver :relay QC, back contactsb of frelay MR, and the winding-of relay ORto terminalN. .ll-lowrofcurrent in this circuitisin th e, proper direction to :cause the relay contacts to vbe picked `up -closngfront contacts \a and -b. When relay C releases, theopeningof-li-ts front contact b vreleases relafy OR and the contacts .ojf "this rel'ay are released to close vback contacts a and b. VDining control codes, however, relay OR is controlled 'by a circuit including iback contact 'd of relay`01T and front contact' [Lof relayMvP, so vthat relay 'DR 'isfopje'r'a'ted 'to'follow 'the cideproduced by thecontacts of relay "0`1'T. "Inj'ir'he'r ra'se, .the animate operation of 'contacts 'aand'b df reiayo'k' between'thir iront and .back positions drives the timing and'c'ountin'g c'h'ain relays 'of coding 'unit -OCU. This causes the code to progress asnescribed inh'e .varius'meiiticned publications. During control cod'e's, 'this operation of r'lay OR vis necessary tofpropeny produce. the code.

'The 'ice is furrherprcviddwith' a'ca'rrier 'transmit 'ter relay 'TC `pIhfis -rla'y is controlled directly b'y .arst transmitter relay '01T overa circuit 'inciur'lingback 'con- .tact e of the lar-'ter relay. l 'It is to be' seen, therefore, that relai/"TC fis nrirnfi'ly energized rii'beconie's'neerrergized to-release its contaefsfwhen'relyotlT'pieks up. "in other words, rei'ayTC is 'released during cdd numbered 'code steps and is energized and .picks up tlingevemnumbered code steps.' Eachrelease of relay`TC"'suppresses the control eariererirreiirbr frequency F1 byM'siiuri-ting the carrier triarisniinerat'its back' Contact `b'. 'Eaeh'su'plsassarese At .the office, vanother relay MCP is used to repeat the operation of relays OM and OC. The circuit for energizing relay MCP may be traced Yfront-terminal 'B over back contact b of relay OC, front contact a of relay MP, andthe winding of relay yMCP to terminal N. It is to be seen, therefore,v that relay MCP follows the coded operation of relay -OC only .when relay MP is picked up, that is, during a control code. As will appear shortly, relay MCP is .thus picked up during each odd numbered step of a control code and is released during even numbered code steps.

A code disagreement relay CD is also included in the circuit arrangement at the olce. This relay is normallly energized over back contact c of relay OM. Thus during reception of `an indication code at the olice, relay CD is continuously energized since relay OM remains released. During control codes, with back contact c of relay OM open, relay CD is held energized over one or the other of its two stick circuits. The nrst of .these stick circuits may be traced vfrom terminal B over front contacts a of relays TC, OC, and CD, and Ithe Winding of relay CD :to terminal N. The second stick circuit is lsimilar -but includes back contacts a of relays TC and OC. Relay ICD..is an ordinary acting relay, but is provided with `a retardation circuit yarrangement which slows the release of this relay under certain conditions, as will be explained shortly. The irst retardation circuit may be :traced :from terminal N .through ,the half-.wave rectiier unit Q1 in its forward .direction over back contact a of relay MCP, front contact a of relay OC, iront contact a, .and .the winding .of relay CD to terminal N. The second and similar retardation circuit includes rectifier Q1, front contact a of relay MCP, and back contact a of relay OC, as well as front contact a and Ithe winding of relay CD.

'The previously mentioned `oilice carrier receiver relay OC is of the biased type and is normally energized by the 'FZ carrier current receiver as long -as can-ier current of trequency F2 is being received from the station. At any `time that this carrier current is suppressed, relay OC is deenergized and quickly releases. The station location is also supplied with a station coding unit. This coding unit is similar to the oilce coding unit OCU and thus is` completely described in either of the previously mentioned publications. It is vherein lback contact a will appear shortly.

The station is also provided with a carrier receiver relay FC which is normally energized by the F1 carrier current receiver, over back contact a of relay FIT, as long as car-rier current of frequency F1 is being received from the otlice. Back contact a of relay FC, when the relay is released, suppresses the F2 carrier current transmitter to )halt the transmission of carrier current of this frequency. Front contact b of relay FC drives a iield line relay FR to follow the coding action of relay FC. Relay FR li-n turn, through its contacts a and b, drives coding unit SCU to receive the control codes in a manner completely described in detail in the previously mentioned publications.

. During the transmission of indication codes, relay FlT operates in the manner usual to such systems to transmit vthe code. Relay FIT controls relay FC during the transmissionof indication codes through its back contact Ia, relay FC being deenergized when this back contact is open. Relay FC then releases .and suppresses the carrier current of frequency F2 by shunting the transmitter F2 during the odd` numbered code steps. Release .of relay FC during indication codes also releases relay FR and the code following operation of this latter relay to alternately operate its contacts a and 'b between their front and back positions drives the timing and counting relay chains of coding unit SCU to produce the indica tion code in the usual manner of such'systems. v y

Weshall now describe the operation of the apparatus during the transmission of a-control code from the oce. In the tat-restjcondition of the apparatus, relays OR, OC, CD, TC, FC, and FR are energized so that these relays are picked up with Ifront contacts closed. When the operator at the ofce initiates a control code, relay OM is energized and picks up. As previously explained, this immediately results in the energization of repeater relay MP which also picks up closing its front contacts. The opening of back contact c of relay; OM interrupts the energizing circuit for relayv CD. However, at this moment, the rst stick circuit for this relay is still complete, this circuit including front contacts a of relays TC and OC. The opening of back contact b and the closing of the corresponding front contact of relay MP transfers the control of relay OR from relay OC to relay 01T over back contact d of this latter relay.

The pickup of relay OM, thus closing its front contact a, completes the energizing circuit for relay 01T, as is more fully explained in eitherof the previously mentioned publications. Relay 01T then picks up, to start the rst step of the control code. The opening of back contact d of lrelay 01T deenergizes relay OR and, since this relay is of the biased type, it immediately releases to -close its back contacts. The opening of back contact e of relay @iT deenergizes relay TC which shortly releases. The closing of back contact b of relay TC suppresses the F1 carrier current transmitter halting the transmission of current of this frequency over the communication channel. This causes the deenergization of relay FC at the station and this biased relay immediately releases to close its back contacts and open its front contacts. The release o-f relay FC, opening its 'front contact b, deenergizes relay FR wat the station and this latter relay also immediately releases.

rEhe closing of front contact c of relay 01T at the start `of the rst code step completes the energizing crcuit for relay 02T, this circuit also including front contact b of relay OM. Relay 02T thus picks up and at its own front contact a completes a -stick circuit. The opening of back contact b of relay 02T interrupts the energizing circuit for Irelay 01T. At the proper time, relay 01T is deenergized by the opening of its stick circuit network in the progress of` the codingaction. Relay 01T, when thus deenergized, releases after its slow `release period and -reenergizes relays OR and TC in an obvious manner. Relay OR immediately picks up to drive the office coding unit OCU to progress the code to the second code step.v When relay TC picks up, the opening of its backV contact b removes the shunt from transmitter F1 and -allows the transmission of carrier current of frequency F1 to resume. This energizes relay FC `at the station since relay FIT at that location is released. The energization of relay FC is followed by the reenergizing of relay FR which picks up to receive the second code step. The coding action continues with relay 01T picking up and releasing to drive the oce -coding unit through relay OR to drive the field cod- This action is completely ,described in the previously mentioned publicat-ions and is here reviewed briefly only to establish a basis for the operation of the circuitsiof our invention.

Each time relay FC releases dueto the suppression of carrier current of frequency F1 by relay TC releasing at the oflice, back contact a of relay FC shunts the carrier current transmitter F2 causing the suppression of carrier current of this frequency and halting its transmission over the communication channely to the: oflce location. The,absenc'e rofk'th'e carrier current Fzfat the ofic'ede'e'nerg'izes relay OC and this relay, being `of the biased type, immediately releases. It is to be vnoted here that lthis releaseofrel'ayOC follows the release of relay TC'as controlled `by oce transmitterrelayitll by only afshortperiod, the delay being due only to the time necessary for the roundtrip of the carrier current, or in this case its suppression, from the `oice to the station and back. The 'release of relayV OC to close its back contact b-'energizesrela'y MCP bycompleting the energizing circuit:includingYback-fcontact 'b of relay OC and front contact a of relay MP, the latter contact, `of course, being closed at this time ldue to the transmission of the control code. y

When relay TC initially releases at the beginning of the rst code step, theopening of front'contact a of this relay interrupts theistick circuit for 'relay CD. However, -the release of relay CD is retarded by a shunt provided by rectifier Q11, the vshunting circuit including back contact a of relay -MCP and front contacts aV of relays OC and CD. When relay OC releases shortly yrecuergiz'ed and holds its vfront contacts closed, or back 9 contacts open, during this normal coding action. The pickup of relay'MCP upon the release ofrelay OC complete's the second shunt circuit for relay CD. This sec 'ondlshunt circuit, as explained, includes back contact a of relay OC and front contact a of relay MCP. The

opening of 'back `contact aof relay MCP during this action interrupts 'the first shunt circuit which initially retarded the release ofrelay CD.

'When relay TC picks upat Ythe beginning ofthe second `code step `the `secondstickcircuit for relay CD is interruptedat 'the back'contact a of relay TC. However, the second shunting circuit above tracedr retards the release of relay CD foral'short period. As previously explained, the pickup of relay TC to open its back contact b removes the shunt 'from the control carrier transmitter and this results in'the energization of' relay .FC atthestation. Opening of backcont'act `z ofrela'y FC- removes the shunt from the indication'carrier transmitter and as a resultrelay OCat the cnice-is reenergized by the reception ofcarrier currentroff-the indication frequency F2. Relay OC picks up,"rele'asing rrelai/.MCP and completing again the rst sti'ckcircuit"'for relay CD, both of these actions having been previously discussed. Under normal operation, relay OC is "reenergized and picks up to close its front contact a prior to the end of theretardation period for relay-'CD -so'th'at 'this latter `relay holds its front contacts 'closed during the entire period. Thus, it fis to be seen that l'code disagreementxrelay CD is not released during tnormalroperation iin transmitting a control code. Rather, vrelay CD feeds on the answer-back signals from the -station lto hold its front contacts closed and back contacts open. This allows the control coding action of -unit OCU to continue vuntil the completion of the control Icode, after which the unit rresets itself and the `entire system. to theinormal Aat-rest condition.

'1f some kind of azline'or communication channel fault- 'occursyeven though temporary in nature, or ifan in- Yducedpulse of current blanks out a code step, relay FC at the station will fail to follow the operation of relay TC 'at `the office in transmittingthe control code.

This causes asimilar failure, as will be obvious from Vthe previous "description, :in the operation of relay OC `to likewise follow the operation of relay TC. Since each operation -ofrelay TC opensrthe then effective stick eireuitvfforlrelay'CD andthe-other stick circuit-'isnot transmission `of the control code from the oce.

completed until relay 0C.i1ikewise `operates 'in a-corresponding manner, the failure of relay OC to lf'ollowthe operation'of' relay TC will result .inV the stick'circuit ynetwork for relay CD remaining open. Relay CD -then releases 'atthe end Vofthe retardation period furnished by rectifier Q1..

it may also occur-that, after the correspondingoperation -of .relays TC and OC at the oce, a spurious pulseiwill be induced into one or theother of the carrier 4circuits which will result inthe operation `of relay OC to its opposite position prior to'the vproper operation of relay TC in the normal 'progress of the code. This again interrupts the stick circuit network for relay CD. Under these conditions, the shunt circuit across the winding vof relay 'CD through rectifier Q1 is open and therefore ineiifective, so that relay CD immediately releases. Thus a line fault or spurious pulse of a very short duration occurring during a code step will result in the release of relay CD and the/halting of the icoding actionyas will `be explained shortly. AIt is to be remembered 'that `relay MCP follows the operation of relay OC so that, upon the reestablishment of the stick circuit network of relayCD, relay MCP has operated to establish -the'retardation ,circuit for the next code step. For example, .consider the relays in the position in which they are shown in Fig. l and to which they 'would operate immediately after the vbeginning of'each even nurn- 'beredode fstep. lf .a l.spurious pulse causeslrelay OC to release, opening its front contact a and closing lits back contact a, the retardation circuit for relay CD over this back contact a of `relay OC is open at front contact a of .relay MCP which released when relay OC picked up. Relay CD thus will immediately release, due to the `interruption 'of the stick circuit network, prior to the time that relay MCP can pick up to reestablish this retardation circuit.

lf relay CD releases as the result of a communication channel interruption or code transmission failure during-an odd numbered code step, relay 01T will be held Aup over the special stick circuit established at back contact c of relay CD. This circuit may be traced from terminal B over back contact c of relay CD, front contacts b and a of relay 01T, land the winding of relay 01T toterminal N. Relay 01T is thus held energized, haltingy the coding action of unit OCU until the coding unit lapparatus drops out Vand resets to its normal at-rcst condition. Such a drop-out and reset action due'to the halting of the code is fully explained in the previously mentioned publications and needl not be here repeated. lf lrelay 'CD releases during an even numbered code step, relay 02T is held energizedover the stick circuit including-back contact b of relay CD and front contact a ofA relay 02T. Again the coding unit apparatus drops out because of the halting of the code and the entire system resets to its normal at-rest condition. In other Words, in either case, the release of relay CD interrupts the coding action of unit OCU, which likewise halts the Since code is therefore no longer received at the station, the station coding unit drops out in synchronism with 'the oce coding unit, the entire system returning to its atrest condition at substantially the same time. Even though progressive registry of control functions is in use, any control function being transmitted by this nal step of the code, that is, the step during which the interruption occurs and the coding action halts, will not be registered at the station since control function registry occurs at 'the beginning of the succeeding code step. Thus the false registry of an improper control function is prevented under these conditions.

Fig. 2 shows the form of our invention as disclosed in Fig, l when a direct current line circuit is used as the communication channel between the ofce and the station. In this figure, only the necessary line circuit connections are` shown VVat o'icey and station which re- 'neta-#Ss place the Aconnections to the carrier communication channel of Fig. 1, the remainder of the circuit arrangement-used with Fig. 2 being identical with that previously `discussed for Fig. l. It is to be noted that the receiver relay FC at the station is provided with two windings ofdifferent resistances. In other words, the upper winding of this relay is of relatively low resistance when-compared with the higher resistance of the bottom winding. It may also be noted that the similar relayFC used at the station in Fig. l may also have different resistances in its two windings, although this is not critical to the operation of the apparatus when carrier communication is used.

The direct current line circuit of Fig. 2 is supplied with energy from a line battery LB at the office location. The `line circuit also includes pole-changing contacts b and c of relay'TC, both windings of receiver relay FC Aat the station, back contact a of station transmitter relay F1Tthe upper winding of oice receiver relay OC, and line wires L1 and L2. It is obvious that, in the at-rest condition shown, line wire L1 has a positive polarity when 'compared with line wire L2. A line resistance R1 at the oiice is included in the circuit connections to limit the line current under all conditions. A second resistance R2 is connected in series with the windings of relay F C at the station. However, this resistance R2 and the bottom winding of relay FC normally are shunted by front contact a of relay FC. Thus the line current during normal at-rest conditions is of a relatively high level and relays OC and FC are energized suiciently to pick up their contacts.

During a normal control code, the release of relay TC during the odd numbered steps pole-changes the polarityof the line circuit so that the normally positive line `wire'Ll becomes negative. However, during the even numbered code steps with relay TC picked'up, line wire .L1 again has a positive polarity when compared with line wire L2. During each odd numbered code step, with theV line circuit from the olllce to `the station polechanged, relay FC releases, since this biased relay, as `previously explained, releases when the flow of current 'through either of its windings is in the direction opposite tothe arrow. The release of relayFC opens its front .contact a, inserting its 'bottom'winding and resistance jRzfinto the line circuit and thus materially reducing the line current. gization `of relay OC to be reduced below the level at "fwhich it willhold its front contacts closed and this latter 'relay also releases. This release of relay OC, or in other words', the reduction of-the line current by the release `ofre'lay FC, constitutes the answer-back from the station, for this type installation, during the odd numbered code steps.

- When relay TC picks up at the beginning of an even numbered code step,` its contacts lb and c return the polarity vof the line circuit to nor-mal. The low level "current still in effect is of the proper direction and, since 'this'current liows through both windings, relay FC is suliiciently energized and picks up. This action of relay FC closes its front contact a, shunting its bottom winding and resistance R2, thus increasing the line current to its normal value again. This increased line current results in the energization of relay OC toa suiiicient level -for 'it-'to' pickflup its contacts. Thus the increase of the line current and resulting pickup of relay OC constitutes lthe vanswer-back vfrom vthe station during the even numbered co'de steps; Y The operation 'of the local circuit arrangement at the oliiceunder this form of installation is the same as pre- -viously discussed for 'the carrier current installation. In other words, the operation of relay OC to lfollow the operation' of relay TC holds the code disagreement relay CID-picked up and allows the control code to continue. Again', itV relay OC fails Vto follow the operation of relay 'TC due to a'- line circuit interruption or i-fa spurious Y This reduced line current causes the enerpulse causes lrelay OC to operate ahead of'. the corresponding operation -of relay TC,v relay CD is released and operates to halt the coding action; It is to be noted, of course, that lthe operation of, relay FC at the station during the control code to alternately open and close its front contact b results in the similar operation of line relay FR and thus the coding unit SCU is driven to receive the control code.

During -an indication code, the operation of transmitter relay FIT at the station alternately opens and closes the line circuit at back contact a of this relay. This results in the alternate releasing and picking up of relay OC at the oiice to drive, through line relay OR, ofiice coding unit OCU to receive the indication code. As before, there is no answer-back during indication codes, relay CD being held energized over back contact c of relay OM. It should be noted, however, unless special circuits are added, that Iwhen the line circuit is reclosed at back contact a of relay FIT, at the beginning of each even numbered code step, relay FCl picks up slightly ahead of relay OC at the office. This occurs because the level of the line current is initially low and is of a value to suiciently energize relay OC only after lfront contact a of relay FC closes. This action may be avoided if afront contact a of the station master relay FM is connected in multiple with front contact a of relay vFCQas shown by the Vdotted connections in the drawing. Since the station master relay, similar in purpose to relay OM at the oice, picks up at the beginning of an indication code, and remains up during the entire code, its front contact a will be closed to shunt the lower winding of relay FC and resistor R2 so that the line current is always at a high level during each even numbered step of an indication code.

The second form of our invention, as shown in Fig. 3, is an adaptation of our invention which is applicable-to installations Where only long code steps are used to carry control functions which are registered at the station progressively during the code or where all control functions transmitted to a station are registered during the, final step of a complete code. A special advantage of this second form of the apparatus is that it does not lrequire any modification of the oliice coding units OCU from the standard lform as shown in the previously 'mentioned Manual 510. Thus, all oice coding units which may be required for a large installation using sev eral channels in dierent directions would be interchangeable and only one type of spare unit would be necessary. In fact, in most innstallations, all coding funits, lwhether intended for the o'iice or the station,

would be interchangeable one with the other if this second form of our invention is used.

`The basic principle of operation previously discussed in connection with Fig. l is the same for the apparatus shown in Fig. 3. Certain changes in the circuit arrangement are made in order to eliminate the modifications to the oice coding unit. The first one of these changes is the additional shunt circuit provided for the carrier current transmitter F1. 'I'his shunt circuit is completed over back contact e of relay CD and thus is elfective when relay CD is released. The energizing circuit for relay OC from the carrier current receiver F2 is carried over front contact d of relay yCD so that this circuit is interrupted any time thatthis latter relay releases; Another change is in the control circuit for relay OR which is effective during control codes. This circuit in this form of the apparatus includes front contact b of relay CD as well as front contact b of relay MP and back contact d of relay 01T. A final change inserts front contact c of relay CD into the energizing circode, vrelays OM and MP arepicked up duringl the entire code. Relay OR is thus driven bythe operation of relay 01Tas previously discussed, as long as relay CD remains held up,fthe alternate openingy and closing of back' con- 1 1 tactd of .relay lTcausing*the.alternatereleaserand pickup-of line relay R. Codingunit OCUds thus driven .by the operation of relay QR to cause the control code .to progress from kone `step to another. .As discussed before, relay TC is released :duringeach odd numbered code-.step by the opening of back contact e of relay 01T. Closing of back contact b 'of relay TC suppresses the `.control carrier current causing the release of relayv FC `at the sta-A code disagreement relay CD, .with the stick circuit neti work ,for this Llatter relay alternately being completed over front contacts a of relays TC and OC and back contacts aof these relays. Relay MCP follows the operation of relay OC, as previously described, to transfer the retardation circuits Vfor relay CD between .itsfront'and back contacts a. Thus as long as the control coding. operation progresses in the normal manner, relay CD.is held-up by the cooperative action of relays TC and OC as influeneed by the answerback indications received from the station due to the operation of relay FC.

lf relay OC fails to follow the operationof relay VTC due to some line interruption or-the'failure of a particular code step to reach the station, the stick circuitnetwork for relay CD remainsopen'for a period .longerthan the-retardation period `established for relayCD. by rectifier Q1 Yand the latter relayreleases. If relay OC should operate ahead of relay TC during an existing code stephecause of a spurious pulse induced into the carrier channel, the stick circuit network for relay CD is-again opened and since, as previously discussed,no retardation circuit is at that time effective for relay CD, this latter relay releases immediately to halt the coding action, laswill be described shortly. Thusvrelay CD is responsive to an induced and erroneous impulse ofvery short duration.

Releaseof relay CD, under either condition, permanently opens its stickcircuit `at.its own front contacta. In addition, the opening of front contact b: of relay CD interrupts the energizing circuit for relay OR whichis effective: during control .codes` and relay OR releases or is.held in its release condition. The opening of front contact c of relay CD interrupts the energizing circuit for relay TC and this latter relay either releases or remains in a released condition. Similarly, ,theopening ofizront contact d oi relay CD interrupts the energizing circuit for relay OC fromtheFZ carrier receiver and relay OCisimmediately released cory is held in .itsreleasedcondition. regardless of subsequent operation of relayFC. The closing. of back contact eof relay CD provides anadditional shunt upon thecar-riercurrent'transmitter 'F1 which4 is efectiveuimmediately to suppressv the carrier currentof frequency lx1-to. endfanveven Vnumbered code step prior tothe subsequentrelease ofirelay TC. .The shuntingof -the control carriercurrent causes. relay `FCat; the station Lorelease followedby .therelease of relay FR. With reiays ORand FR both released or v heldfreleased,.the coding unitsat the oicerand thestation. are settoxthe next odd numbered code step vor'areheld upon theexisting `odd numbered code step, respectively, `depending upon Vthe code step during-which the release of relay CD occurs. -lnv either event, the'entiref system resetsv under the. condition of a code halted duringran odd numbered step. .Relay CD is reenergizedwhenrelay'OM releases to -close its back contact c at the .completion -of the reset-action.

vAsiexplained. above, iffthe release of-.relay vCD occurs during an evennumbered. code step,.the codingunitrsnare ,advanced tothe .nextodd numbered-.co'desteptby thefre- Vcontrolfsystems of the general type here shown. -answeraback pulse received Yfrom the station uponthe lease-.ofthe line .relays ateach location. However, 4this cannot Ycause-the improperregistration of a 4controliunction even though such functions are being registered. progressively during the code. The system shown in Fig. 3, as r.previously'rnentioned, is limited to the progressive registration ofY control functions carried `by long .code steps only. Thus the cutting oi of an evennumbered code stepby the release of relay CDand the stepping of ,the units to-the next oddnurnbered codejstepresults in the reception of the evennumbered code `step ,at the station as a short step. Thus no controLfunction isindicated Yor registered. Of course,.if.t'he.iinal registryof all control functions is held and accomplished only during the nal step of a complete code, .no control function registry at all occurs `during a `code interrupted due to improper transmission. Thus the circuits of the lsecond .form'of our .invention protect Vagainst improper registry of control functions, to the extent of the limitations applied to 1 this .form of the apparatus.

ln Fig.. 4-we have shown the application of the apparatusof the second 4formof our invention to adirect currentline circuit. These line circuit connections here shown arervery similar to those shown in Fig; 2. The only change is the insertion ofafront contact (i vof relay CD in Vthe-linecircuit connections at the office location. As .inFig..2,.only.the line .circuit connections are `shown in Fig. ,4, theremainder of the apparatus beingidentical lwith thatalready shown anddiscussed in Fig. 3. Likewise, the operation of the apparatus when adirect current line circuit is used is very similar to that already discussed for the showing of Fig. 2 andneednot be discussed again .in detail. If relay CD is released due to the improper transmission of .a control code and ,the

lack. offa proper answer-back pulse lfrom the station, its

rfrontcontact d opens to deenergize the entire line circuit. This releases relays OC and FC at once. Again each `coding unit, responsive to the release of the corresponding line relay, holds on the existing oddnum- Ybered code Ystep or, if relay CD is released during an even -numbered code step, steps to the nextodd Vnumberedcode step. Here the coding action is halted ,and the system resetsto its normal at-rest condition. As previously discussed in connection with Fig. 3, theimproperregistry of control functions is thus prevented.

It has beenrdescribed, therefore, how the system of ourfinvention in either of its lforms provides for a check of the proper transmission of control codes in remote The proper reception of each-stepy of-the controlcode assures the oicelocation that the control step has been properly receivedand allows the code to'continue to completion. It there is no reception of the control code stepat-,the station, if there isan improper reception, or if someimproperaction .occurs in the communication channel, the lack of :a proper answer-back immediately causes the coding. action toV behalted. Thisalso preventstheregistry of any control function which would causeanimproper action at the station. VThis is trueeven thoughthe control codev is being registered progressively as. the codingl actioncontinues. Thusrthesystem of ourA invention assures that the desired control actions at the station -tion has dealt specifically with the provision of=,.answer back indications during control codes, thatsimilar arrangementsmaybe used to: check'the vtransmission rof -indicationcodes from the station. .In other Words, the

system of our invention may beapplied to'provide,;at any location-,originating a code a check as to the proper reception of that code at its intended destination, the check beingaccomplished through the medium of =a Vsimultaneous answer-back code originating atthe. receiv i'ng station. Unless the answer-back indicates thateach code step has been properly received, the transmission of the 'code is interrupted and the registry of incorrect functions prevented.

' ,Furthermore, although we have herein described and lshown but two forms of apparatus embodying our invention, it is to be understod that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim l. In a remote control system including at least a first and a second location connected by a communication channel, said first location `being provided with coding ,I

apparat-us having connections to said channel for transmitting stepped codes to said second location, each code step havin-g a particular selected time length, the combination comprising, means at said second location having connections to`said channel for retransmittingv to said first location a code step identical to the received code step in selected .-ti-me .length simultaneously with the reception of each code step from said first location, receiving means at said first location having connections to said channel. for-receiving the .retransmitted code steps; disagreement means at said first location controlled lby said coding apparatus and by saidreceiving means for detecting disagreement in timelength between each transmitted code step and the corresponding retransmitted Y code step, said disagreement means having other connections for halting the operation of said coding apparatus if disagreement is detected; retardation means having connections tosaid disagreement means for compensating for the transmission delays of said channel between the transmission of a code step and the reception of the corresponding retransmitted code step, and other means controlled by said receiving means for cancelling the compensating effect of said retardation means after a retransmitted code step is received to detect interference induced in said channel which interrupts the selected time length of a code step.

2. In a remote control system including an ofiice and at least one station connected by a communication channel, said office being equipped with a coding unit to transmit stepped control codes over said channel which said station is adapted to receive, each code step having a particular selected time length, the combination comprising, a code disagreement relay at said office effective when deenergized to halt the transmission of a control code, an energizing circuit and a stick circuit network for said relay, said energizing circuit including a normally closed contact which is open during the transmission of control codes; said stick circuit including a first pair of contacts alternately closed during the transmission of successive control code steps, a second and a third pair of contacts alternately closed in response to the reception of successive code steps each retransmitted back from said station simultaneously with the-reception at said station of successive ones of said control code steps, and a half-wave rectifier; said first and said second pairs of contacts cooperating during the transmission of a control code to maintain said disagreement relay energized -only if each received retransmitted code step is identical in selected length with the corresponding transmitted control code step, said second and said third pairs of contacts cooperating during a control code to -connect said rectifier at times in multiple with the winding of said relay to retard the relay release to compensate for transmission delay periods in the coordinated operation of said first and said second pairs of contacts and to disconnect said rectifier to cancel the retardation of said relay if said second pair of contacts operates to its other position prior to the corresponding operation of said first pair of contacts as a result of induced extra code steps.

, 14. f 3. In combination with a coding unit at the ofce location of a remote control system, said system also includin-g at least one station connected to the office by a communication channel, said coding unit being capable of lproducing control codes comprising a plurality of successive code steps each having a particular selected time length and including a transmitter relay arrangement havingV connections to said channel to. transmit said code 'steps over said channel, said station being capable of receiving said codes and simultaneously retransmitting each code step in identical time length form as received overV said channel to said oice; a code disagreement relay effective when released to interrupt the operation of said transmitter relay arrangement,v an energizing circuit and a stick circuit network for said disagreement relay; said energizing circuit including a normally closed contact which is opened during control codes, said stick circuit networkv including a first pair of contacts alternately closed during'successive code steps in response to the operation of saidtransmitter relay larrangement to transmit a control code, a second and third pair of contacts'each alternatelyclosed in response to the reception at said office of the successive retransmitted code steps,

and l'a half-,wave rectifier; said first and said second pair of contacts cooperating during a control code tomaintain' said stick circuit network completedonly if each retransmittedcode step is4 identical in time length with the corresponding transmitted control code step, said second and -said'third pairs of contacts cooperating during a control code to connect said rectifier in multiple with said disagreement relay over contacts of these pairs to retard the release of said disagreement relay while said stick circuit network is interrupted between the corresponding operation of said first and said second pairs of contacts during transmission delay periods, said third pair of contacts being effective to interrupt said multiple connection 'if said second pair of contacts operates to its other position prior tothe corresponding operation of said first pair of contacts as a result of an erroneous code step induced into said channel.

4. In a remote control system including at least a -first and a second location, said first location beingprovided with coding apparatus for transmitting stepped codes which said second location is capable of receiving, each code step having a particular selected time length, the combination comprising, a receiver relay of the biased type at said second location having a first and a second winding, said second winding having a higher resistance than said first winding; a line circuit including a source of direct current energy, two line wires extending between said first and second locations, both windings of said receiver relay, and pole-changing contacts responsive to the operation of the coding apparatus, said pole-changing contacts being effective to transmit code steps by altern ately pole-changing the relative polarity of said line wires; a shunt circuit including a normal energy position contact of said receiver relay and connected in multiple with said second winding of said receiver relay, said shunt circuit being effective to materially change the current flowing in said line circuit when said receiver relay periodically operates due to the pole changing action of said pole-changing' contacts to produce an answer-back code step at said4 first location having a time length identical to that of the corresponding transmitted code step, receiving means at said first location having connections to said line circuit for receiving the answer-back code steps, disagreement means at said first location controlled by said coding apparatus and by said receiving means for detecting disagreement in time length between each transmitted code step and the corresponding answer-back code step, said disagreement means having other connections for halting the operation of said coding apparatus if disagreement is detected; retardation means having connections to said disagreement means for compensating for the transmission delays of said line circuit between the --transrnisfsionrof' .a ,code step 4`and the reception of the corresponding ausfvverfback 'code .SQIL and othery meansrcontro'lled bysadreceiving vmeans for cancelling the .compensating effect of said retardation means after an answerfbaokcodemstep is lreceivedto Ydetect interference induced in .said channel which interrupts theselected timelength of Aa codestep.

5. In a remote control system .includinggan Ofe and at leastonevstation, 4said ofce being provided Withcod ing ,apparatus for transmitting steppedcode's which-said station is capable of receiving, each Code step hav ng a particularselected timel length, the cmbinatinlcomprisin'g, yam Oice receiver Arelay, 'Sttih 'CC'CYCI lfcrlfy of 'the'bi-as'ed type having fa lfirst and 'a 'second winding, said second winding having a higher resistance than-said frst winding; a line circuit including .a source of direct current energy atsaid oincetwoline wires Ventertaingibietween said oil-ice and said station, the winding of lsaid olce receiver relay, both windings of 'saidjstation receiver relay, e resistor, 'and pole-changing contacts 'responsive to the operationof said oflic'e coding apparatus Atotransmit successive code steps by alternately pole-changiugjthe polarity of the energy applied to said line Wires; a shunt Lcircuit including a normal energylposition Contact of said stati-en receiver relay cennecte'r'r in multiple with said l resistor and'said second winding of'saidstation lreceiver' relay in seriessaid'shunt circuit being effective vto "Ina- Yteriall'y 'change the current Yflowing in said 'line circuit transmitan answer-back codestep havng'a time 'length identical to that of the eorrespondingtansinitted code Y 16 Sleep .each Atime-saidstation .receiver relay periodically operates Anue ,to the pdlefchanging ofthe pelarityef ,said line lc'rc'l'lit .Said oce t, receiver relay 'being responsive vto each change 'of line circuit current 'to receive ythe 'answer'- backvcode steps, disagreement means at 'said oiii'ce 'controlled by said "coding apparatus Tand by said ce receiver relayfor detecting disagreement in time length between eachi't'iar'lsmit't'ed code 'step andthe corresponding answerfcbackcode stein-said disagreement means having'v ference induced in lSaid channel Kwhich :interrupts the 

